1. Field of the Invention
The present invention relates to a solid-state image sensor having a plurality of pixels and a camera including the sensor.
2. Description of the Related Art
In a solid-state image sensor having a plurality of pixels, part of the charge generated in a given pixel by photoelectric conversion sometimes mixes in an adjacent pixel. This may affect a signal from the adjacent pixel. Many color solid-state image sensors, in particular, use a Bayer arrangement as a pixel arrangement. In a Bayer arrangement, adjacent pixels output signals with different colors. In color solid-state image sensors, the phenomenon in which charge leaks out to adjacent pixels is called mixture of colors. There is known a structure in which, in order to reduce the mixture of colors, an impurity region serving as a potential barrier for signal charge is formed under an element isolation region located at the boundary between adjacent pixels (Japanese Patent Laid-Open No. 2003-258232).
In a CMOS solid-state image sensor in which each pixel has a floating diffusion, as a given pixel shrinks, the width of an element isolation region made of an insulator to isolate adjacent pixels from each other can decrease. With a decrease in the width of an element isolation region, the width of an impurity region forming a potential barrier under the element isolation region decreases, resulting in a degradation in preventive effect for mixture of colors.
Increasing the width of an impurity region to more than that of an element isolation region in order to form a sufficient potential barrier will suppress the depletion layer of a photodiode adjacent to the element isolation region and decrease the effective area. This leads to a decrease in saturated output. In addition, improving the effect of a potential barrier by increasing the impurity concentration without increasing the width of the impurity region will spread the impurity in the lateral direction and prevent the spread of the depletion layer of an adjacent photodiode. This leads to a decrease in effective area.